Electromagnetic wave detector, electromagnetic wave detector array, and electromagnetic wave detection method

Abstract

An electromagnetic wave detector comprises: p-type and n-type graphenes arranged side by side on an insulating layer; a first electrode and a second electrode opposing each other via the graphenes; a gate electrode for applying an operation voltage to the p-type and n-type graphenes; a balance circuit connected between two second electrodes; and a detection circuit. The p-type graphene has a Dirac point voltage higher than the operation voltage. The n-type graphene has a Dirac point voltage lower than the operation voltage. In a state in which no electromagnetic wave is incident on the graphenes, the balance circuit places the first electrode and the second electrode at the same potential. In a state in which an electromagnetic wave is incident on the p-type and n-type graphenes, the detection circuit detects an electric signal between the second electrodes, and outputs an electric signal in the state in which the electromagnetic wave is incident.

The invention claimed is: 
     
       1. An electromagnetic wave detector for converting an electromagnetic wave into an electric signal and detecting the electric signal, comprising:
 a substrate; and 
 an insulating layer provided on the substrate, and 
 further comprising the following (a) or (b): 
 (a) p-type and n-type graphenes juxtaposed on the insulating layer; 
 a first electrode and a second electrode disposed facing each other with the p-type and n-type graphenes interposed,
 the first electrode being one electrode electrically connected to both the p-type and n-type graphenes at one ends, 
 the second electrode being two electrodes electrically connected to other ends of the p-type and n-type graphenes, respectively; 
 
 a gate electrode that applies an operation voltage to the p-type and n-type graphenes; 
 a balance circuit connected between the two second electrodes; and 
 a detection circuit that detects electric signals between the two second electrodes, 
 wherein the p-type graphene has a Dirac point voltage higher than the operation voltage, and the n-type graphene has a Dirac point voltage lower than the operation voltage, 
 in a state in which an electromagnetic wave is not incident on the p-type and n-type graphenes, the balance circuit makes the first electrode and the second electrode have an identical potential, 
 in a state in which the electromagnetic wave is incident on the p-type and n-type graphenes, the detection circuit detects electric signals between the second electrodes, and 
 the electric signals in the state in which the electromagnetic wave is incident are output, 
 (b) a graphene provided on the insulating layer; 
 a first electrode and a second electrode disposed facing each other with the graphene interposed, the first electrode electrically connected to one end of the graphene, and the second electrode electrically connected to another end of the graphene; 
 a gate electrode that applies a gate voltage to the graphene, the graphene becoming hole conductive when the gate voltage is V OP1  and electron conductive when the gate voltage is V OP2 ; and 
 a detection circuit that detects electric signals between the first electrode and the second electrode, 
 wherein in a state in which an electromagnetic wave is not incident on the graphene, electric signals when the gate voltage is V OP1  and V OP2  are detected, 
 in a state in which the electromagnetic wave is incident on the graphene, electric signals when the gate voltage is V OP1  and V OP2  are detected, and 
 a difference in the electric signals when the gate voltage is V OP1  and a difference in the electric signals when the gate voltage is V OP2  between the state in which the electromagnetic wave is incident and the state in which the electromagnetic wave is not incident are obtained respectively, and a sum of these two differences are obtained and output. 
 
     
     
       2. The electromagnetic wave detector according to  claim 1 , further comprising: a memory circuit that stores an output when the electromagnetic wave is not incident,
 wherein when the electromagnetic wave is irradiated, a difference between a value stored in the memory circuit and the detected electric signal is output. 
 
     
     
       3. The electromagnetic wave detector according to  claim 1 , wherein the balance circuit is a bridge circuit in which the p-type and n-type graphenes and two or more resistance elements are combined or a bridge circuit in which either one of the p-type and n-type graphenes and three or more resistance elements are combined. 
     
     
       4. The electromagnetic wave detector according to  claim 3 , wherein the resistance element is configured by one or more elements selected from a group consisting of a semiconductor thin film transistor element, a thin film resistance element, a two-dimensional material transistor element, a transistor element using the p-type graphene, and a transistor element using the n-type graphene. 
     
     
       5. The electromagnetic wave detector according to  claim 1 , wherein a differential amplifier circuit is used as the detection circuit, and a differential current at a time of electromagnetic wave irradiation output from the first electrode electrically connecting the p-type and n-type graphenes in series is used as an input of the differential amplifier circuit. 
     
     
       6. The electromagnetic wave detector according to  claim 1 , wherein the gate electrode is provided on an insulating layer provided on the graphene or provided under an insulating layer provided under the graphene, and a voltage is applied to the graphene from the gate electrode. 
     
     
       7. The electromagnetic wave detector according to  claim 1 , further comprising: a contact layer provided in contact with the graphene on or under the graphene, wherein the contact layer supplies holes or electrons to the graphene. 
     
     
       8. The electromagnetic wave detector according to  claim 7 , wherein the contact layer is made of a material that causes an electric field change due to electromagnetic wave irradiation. 
     
     
       9. The electromagnetic wave detector according to  claim 7 , wherein the contact layer is selected from a group consisting of quantum dots, ferroelectric materials, fullerenes, liquid crystal materials, and plasmon antennas. 
     
     
       10. The electromagnetic wave detector according to  claim 1 , wherein the graphene is selected from a group consisting of one-layer graphene, two or more layers of laminated graphene, graphene nanoribbons, and a two-dimensional material having one-layer or a laminated structure. 
     
     
       11. The electromagnetic wave detector according to  claim 1 , further comprising: a correction circuit that detects current values or voltage values of the p-type and n-type graphenes when the electromagnetic wave is not incident, and corrects the values as needed so that the p-type and n-type graphenes have an identical resistance value. 
     
     
       12. The electromagnetic wave detector according to  claim 1 , wherein a light shielding portion is provided in an optical path of the electromagnetic wave incident on either one of interfaces between the graphene and the first electrode or the second electrode. 
     
     
       13. An electromagnetic wave detector array in which the electromagnetic wave detector according to  claim 1  is set as one pixel, and the pixels are arranged in an array shape. 
     
     
       14. The electromagnetic wave detector array according to  claim 13 , wherein four electromagnetic wave detectors having different longitudinal directions of the graphene by 45° each are set as pixels and arranged in an array shape. 
     
     
       15. An electromagnetic wave detection method, in which a p-type transistor having a channel of a p-type graphene having a Dirac point voltage at a gate voltage higher than an operation gate voltage, and an n-type transistor having a channel of an n-type graphene having a Dirac point voltage at a gate voltage lower than the operation gate voltage are connected in series, and electric signals at both ends thereof are detected, comprising:
 applying the operation gate voltage to the p-type transistor and the n-type transistor in a state in which an electromagnetic wave is not incident on the p-type graphene and the n-type graphene, and controlling a resistance value of the channel of the p-type graphene and a resistance value of the channel of the n-type graphene so as to become identical; 
 detecting the electric signals in the state in which the electromagnetic wave is not incident on the p-type graphene and the n-type graphene; 
 detecting the electric signals in a state in which the electromagnetic wave is incident on the p-type graphene and the n-type graphene; and 
 obtaining and outputting a difference in the electric signals between the state in which the electromagnetic wave is incident and the state in which the electromagnetic wave is not incident. 
 
     
     
       16. An electromagnetic wave detection method for detecting electric signals at both ends of a transistor having a channel of graphene, in which the graphene becomes hole conductive when a gate voltage of the transistor is V OP1  and becomes electron conductive when the gate voltage is V OP2 , comprising:
 detecting the electric signals when the gate voltage is V OP1  and V OP2  in a state in which an electromagnetic wave is not incident on the graphene; 
 detecting the electric signals when the gate voltage is V OP1  and V OP2  in a state in which the electromagnetic wave is incident on the graphene; and 
 obtaining a difference in the electric signals when the gate voltage is V OP1  and a difference in the electric signals when the gate voltage is V OP2  between the state in which the electromagnetic wave is incident and the state in which the electromagnetic wave is not incident, respectively, and obtaining and outputting a sum of these two differences. 
 
     
     
       17. The electromagnetic wave detection method according to  claim 15 , wherein the electric signal is a current or a voltage. 
     
     
       18. The electromagnetic wave detection method according to  claim 16 , wherein the electric signal is a current or a voltage.